Suffocation leaves a mark in the genes

A murderer could leave a telltale genetic fingerprint in their victim's genes, say researchers in Japan, helping forensic sleuths to identify how they were killed.

Experts often struggle to diagnose whether someone died by strangulation or suffocation, rather than by some other means. In some cases, the crime scene or marks on the body make the case clear cut; in others there are no such clues.

Now a team at Nagasaki University has shown that a person's own genes might help to reveal how they met their end. Kazuya Ikematsu and his colleagues anaesthetized and then killed two small groups of mice, by either strangulation with a string, or by decapitation. They dissected skin samples from the animals' necks and compared the activity of a broad spectrum of genes inside the skin cells, by looking at the amount of RNA pumped out by those genes.

The researchers found four genes that were more active in the strangled animals than those that had died suddenly. Their findings are accepted for publication in the journal Legal Medicine1.

The study adds to emerging evidence that gene activity could be a useful clue in pinpointing the time or cause of death. It's a direction that could prove very useful in forensics, says pathologist and molecular biologist Edward Gabrielson of Johns Hopkins University in Baltimore, Maryland. "The concept of using molecular markers in forensic pathology is interesting and potentially very powerful," he says.

Under pressure

Future studies could identify a battery of genes or proteins whose levels of activity are consistently boosted or cut when the skin is under pressure or deprived of oxygen, Gabrielson suggests. In human cases, pathologists could screen tissue for this molecular signature and use it, alongside more traditional techniques, to help pin down the cause of death.

Such a technique would be particularly valuable in cases of sudden infant death syndrome, says Greg G. Davis, a medical examiner and forensic pathologist at the University of Alabama, Birmingham. It could help to reveal whether a child suffocated on their bedding or died for other reasons. "That alone would be extraordinarily useful," he says.

Presently, forensic pathologists rely largely on case histories, including the situation in which a body is found, plus gross examinations and scrutiny of the tissues. In the case of suffocation, examiners look for bruises, damage to delicate neck cartilage and tiny burst blood vessels in the eyes.

But because these signs can be subtle or missing entirely, some cases of suffocation and strangulation "can be an extremely difficult or subtle diagnosis," Davis says. "People have been searching for a magic test for asphyxiation for decades."

Body of evidence

Davis and Gabrielson caution that far more extensive studies must be done before molecular methods can be routinely used on human bodies.

One obstacle is that they must deal with the natural variations in gene activity between each person and those caused by genetic or protein material decaying since the time of death. "I don't see anyone being put in jail based just on this," Davis says.

And medical examiners may be reluctant to adopt new techniques if they think old ones will suffice. "It takes effort to start moving a field in new directions," Gabrielson adds.